Measurement of the positions of centres of curvature of optical surfaces of a single or multi-lens optical system

ABSTRACT

In a method for measuring the positions of centers of curvature of optical surfaces of a single- or multi-lens optical system, an imaging lens system images an object plane into a first and a second image plane. The first image plane is produced by a first ancillary lens system having a first focal length and defining a first beam path, while the second image plane is produced by a second ancillary lens system having a second focal length that is different from the first focal length and defining a second beam path that is different from the first beam path. An object arranged in the object plane is then imaged simultaneously or sequentially at the first and the second image plane by means of measuring light. Reflections of the measuring light at optical surfaces of the optical system are detected by means of a spatially resolving light sensor. The actual positions of the first and the second center of curvature are calculated from the detected reflexes.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation application of U.S. patent application Ser. No.14/978,208 filed Dec. 22, 2015 that claims benefit of earlier EuropeanPatent Application No. 14 004 425.6 filed Dec. 24, 2014. The contents ofthese earlier applications are incorporated herein by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The invention relates to a method and a device for measuring thepositions of centres of curvature of optical surfaces of a single- ormulti-lens optical system.

2. Description of the Prior Art

In the manufacture of high-quality multi-lens optical systems, thelenses must be aligned relative to one another with high accuracy. Inorder to be able to carry out such alignment, it is necessary todetermine the positions of the optical surfaces by measurement. Even ifthe position accuracy is not checked during alignment of the lenses,such measurements are routinely carried out at least within the scope ofquality control.

An important geometrical parameter in the measurement of multi-lensoptical systems is the positions of the centres of curvature of theoptical surfaces. Ideally, the centres of curvature lie exactly on acommon reference axis, which should generally coincide with the axes ofsymmetry of the lens mounts holding the lenses. In real optical systems,however, the centres of curvature are distributed randomly about thatreference axis as a result of manufacturing and mounting tolerances. Ifthe distances of the centres of curvature from the reference axis aretoo great, the imaging properties of the optical system deteriorateintolerably.

From DE 10 2004 029 735 A1 there is known a method for measuring centresof curvature of optical surfaces of a multi-lens optical system, whereinthe positions of the centres of curvature of the individual opticalsurfaces are measured in succession by means of an autocollimator. Foreach optical surface, the measurement is preferably carried out severaltimes at different azimuthal angular positions of the optical system.The first surface for which the position of the centre of curvature ismeasured is the surface that is closest to the autocollimator. As soonas the position of the centre of curvature of this first surface hasbeen determined, the subsequent second surface is measured. However, thefirst surface influences the measurement of the second surface. Theoptical effect of the first surface must therefore be taken intoconsideration mathematically when determining the position of the centreof curvature of the second surface. When taking into consideration theoptical effect of the first surface, recourse is made to the design dataof the first surface, in particular to the desired radius of curvatureand the desired distance from the second surface (that is to say thecentre thickness of the first lens). The previously measured position ofthe centre of curvature of the first surface is additionally taken intoconsideration mathematically.

The same procedure is followed for all further surfaces. Accordingly,the measured positions of the centres of curvature of all precedingoptical surfaces and, in addition, the design data are taken intoconsideration in the mathematical evaluation.

In this known method, the centre of curvature of an optical surface tobe measured must always be situated in the image plane of theautocollimator, whereby the refractive effect of any optical surfaces ofthe optical system situated upstream in the beam path is to be takeninto consideration. It is thus ensured that the measuring light strikesthe optical surface to be measured perpendicularly and is reflected backon itself. Only then is the measuring object of the autocollimator,which can be, for example, a cross-wire, imaged sharply on a spatiallyresolving light sensor of the autocollimator. After each measurement ofthe position of a centre of curvature, the focal length of theautocollimator must therefore be readjusted. In general, this is carriedout by displacing one or more lenses along the optical axis of theautocollimator.

In particular in the case of industrial measuring tasks, where a verylarge number of optical systems of the same type are to be measured in ashort time, a considerable portion of the total measuring time is takenup by this repeated adjustment of the focal length.

Similar problems also arise when measuring the two centres of curvatureof a single lens, for example in order to determine its optical axistherefrom. Here too, the focal length must be altered once for eachmeasuring operation.

SUMMARY OF THE INVENTION

Accordingly, the object of the present invention is to provide a methodwith which the positions of centres of curvature of optical surfaces ofa single- or multi-lens optical system can be measured accurately andvery quickly. It is a further object of the invention to provide adevice with which such a method can be carried out.

With regard to the method, the object is achieved by a method formeasuring the positions of centres of curvature of optical surfaces of asingle- or multi-lens optical system, which method comprises thefollowing steps:

-   -   a) providing an imaging lens system which images at least one,        and preferably exactly one, object plane into a first image        plane and a second image plane which is different therefrom;    -   b) so arranging the optical system that, taking into        consideration the refractive effect of any optical surface of        the optical system situated upstream in the beam path, a        supposed position of a first centre of curvature is situated in        the first image plane of the imaging lens system and a supposed        position of a second centre of curvature is situated in the        second image plane of the imaging lens system;    -   c) simultaneously or sequentially imaging an object arranged in        the object plane at the first and at the second image plane by        means of measuring light which strikes the optical system from        one side;    -   d) detecting reflections of the measuring light at optical        surfaces of the optical system by means of a spatially resolving        light sensor;    -   e) calculating the actual position of the first and of the        second centre of curvature on the basis of the reflections        detected in step d).

The invention is based on the observation that the rapid measurement ofthe positions of centres of curvature of two or more optical surfacesdoes not require a plurality of imaging lens systems that are whollyindependent of one another. If there is used an imaging lens systemaccording to the invention which, by means of portions of the measuringlight that are separated spatially, according to wavelength or accordingto polarisation, produces a plurality of image planes in the same beampath which are generally not optically conjugated, movements of opticalelements can be avoided with a low outlay in terms of construction. Thisis a prerequisite for quick measurement, because movements generally donot permit quick measurement of the centres of curvature.

Before the actual measurement, the position of the image planes must beadjusted to the supposed positions of the centres of curvature. Afterthis adjustment, optical systems of the same type can be measured veryquickly in a large number, because no lenses or other optical elementsin the imaging lens system have to be moved in the axial direction oncethe imaging lens system has been adjusted or set up.

The spatially resolving light sensor is preferably situated, providedthat there is a reflecting surface in the first or in the second imageplane, in a further image plane which is optically conjugate to thefirst and the second image plane.

It is generally sufficient if only a single light sensor is provided.That light sensor then detects the reflections from a plurality ofoptical surfaces simultaneously. The reflections can generally bedistinguished from one another by simple measures, which will bedescribed in greater detail below. In principle, however, it is alsopossible to provide a plurality of light sensors in order, for example,separately to detect the portions of the measuring light that areseparated spatially, according to wavelength or according topolarisation. Those light sensors are then preferably arranged atoptically mutually corresponding positions. In particular, the lightsensors can be arranged optically equally far from the imaging lenssystem. “Optically equally far” is here understood as meaning that theoptical path length, which, unlike the geometrical path length, takesinto consideration the refractive indices of the media through which thelight travels, is equal for all distances between the imaging lenssystem, on the one hand, and the light sensors, on the other hand.

The same applies correspondingly also to the object. Here too, it isgenerally sufficient if only a single object plane is provided, in whichan object is situated. The division of the measuring light into aplurality of portions that are separated spatially, according towavelength or according to polarisation then does not take place untillater in the beam path. It is, however, also possible to provide aplurality of object planes, which can be associated with said portionsof the measuring light. Here too, it is generally expedient for theobject planes to be situated at mutually optically correspondingpositions. In particular, they can be arranged optically equally farfrom the imaging lens system.

In general, it is expedient if, when measuring the position of a centreof curvature of a surface lying within the optical system, the measuredpositions of the centres of curvature of the surfaces lying between thatsurface and the imaging lens system are taken into considerationmathematically, as is known in the prior art. However, suchconsideration can sometimes be dispensed with, for example if therefraction at the preceding surfaces is very small due to smallcurvatures or small refractive index differences, or if the methodaccording to the invention is being used only for the qualitativemeasurement of the positions of the centres of curvature.

In conventional measuring methods, the optical system to be measured isrotated about a precisely determined axis of rotation. That axis ofrotation represents a common reference axis for all the opticalsurfaces, the position of which reference axis is known exactly.Intrinsic measuring errors, which can be attributable, for example, toimaging errors of the imaging lens system, can thus be eliminated.

It is possible to dispense with rotating the optical system to bemeasured if a calibration measurement is carried out before the centresof curvature are measured, from which calibration measurement anallocation of locations on the light sensor with centres of curvature isderived. In this manner, imaging errors of the imaging lens system andalignment tolerances of other components of the measuring setup can betaken into consideration. When the positions of the centres of curvatureare measured, no components are then moved axially during steps c) andd). The entire measuring operation can as a result be carried outextremely quickly. The method can accordingly also be used in connectionwith the alignment or quality testing of optical systems which areproduced in large numbers in an industrial process.

One possibility for such a calibration measurement consists in measuringan optical reference system in which the positions of the centres ofcurvature are known. The reference system is preferably an opticalsystem which is substantially identical to optical systems that arelater to be measured in a larger number. The positions of the centres ofcurvature of the reference system are determined highly accurately inanother external measuring device. Those positions are then associatedwith the positions that are determined as centres of curvature by themeasuring device according to the invention.

Alternatively or in addition, in the calibration measurement thepositions of the centres of curvature of a calibration test piece inwhich the positions of the centres of curvature are unknown can bemeasured in a plurality of azimuthal angular positions of the opticaltest system. Measurement in a plurality of angular positions gives theposition of the centre of curvature in the manner known per se in theprior art, which is then associated with the location of the reflectionon the light sensor. Here too, it is advantageous if the calibrationtest piece is an optical system which is substantially identical tooptical systems that are later to be measured in a larger number.

A further possibility for the calibration measurement consists inmeasuring, using an external measuring system, the locations at whichimages of an object imaged by the imaging lens system form in the firstand in the second image plane. Imaging errors of the imaging lens systemcan thus be detected directly and can be taken into considerationmathematically when measuring the positions of the centres of curvature.

In order to be able to dispense with movements of optical elements ofthe imaging lens system, the first and the second image plane must lieat the supposed positions of the centres of curvature of the opticalsurfaces to be measured, whereby the refractive effect of opticalsurfaces of the optical system situated upstream in the beam path isoptionally to be taken into consideration. The supposed positions of thecentres of curvature are known from the design data of the opticalsystem to be measured. If a different optical system is to be measured,this generally requires the imaging lens system to be adjusted, sincethe first and the second image plane are then situated at differentaxial positions. The imaging lens system should therefore compriseadjustable optical elements, at least in the case of measuring systemswith which a plurality of different optical systems can be measured.

One possibility for producing two different image planes of a singleobject plane consists in producing the first and the second image planeby means of ancillary lens systems with different focal lengths. Thelight paths of the ancillary lens systems are separated by means offirst beam splitters arranged before the ancillary lens systems in thelight propagation direction and combined by beam combiners arrangedafter the ancillary lens systems in the light propagation direction. Inorder to be able to change the position of the image planes, theancillary lens systems as a whole or parts thereof can be arranged to beaxially displaceable.

Another possibility for producing different image planes consists inproducing the first and the second image plane in different azimuthalsegments, which do not overlap in the region of a collimated beam path,of a measuring light aperture associated with the measuring light. Suchsegments can be produced, for example, by a special lens which consistsof two halves with different focal lengths which are joined together.Where there are more than two different image planes, the number ofdifferent segments increases correspondingly.

It is further possible to produce the first and the second image planein different radial segments, which do not overlap in the region of acollimated beam path, of a measuring light aperture associated with themeasuring light. To that end, the imaging lens system comprises, forexample, a lens which has a greater refractive power in a circularcentral region than in a surrounding annular outer region. A similareffect is achieved if two lenses having different diameters are arrangedclose together, so that a portion of the measuring light passes throughboth lenses and another portion passes through only one lens.

In the variants described above, the measuring light is separatedspatially into different portions. As a further alternative it isproposed to produce the first and the second image plane for measuringlight of different wavelengths, that is to say an image plane is clearlyassociated with each wavelength range, so that the measuring light isdivided into different portions according to wavelength. The dispersionof optical elements is thereby used. Chromatically uncorrected lenseshave a longitudinal chromatic aberration, which has the result, forexample, that the image planes for red light and blue light aredifferent. If a mixture of red and blue light is used as the measuringlight, two different image planes are obtained. This approachadditionally ensures that the reflections on the spatially resolvinglight sensor can be distinguished from one another without difficulty,because the reflections have different colours.

In the case of lenses, however, the longitudinal chromatic aberration isgenerally so small that only closely spaced positions of centres ofcurvature can be measured. In the case of diffractive optical elements,the refractive effect generally depends to a much greater extent on thewavelength used. The imaging lens system therefore preferably comprisesat least one diffractive optical element or a hybrid lens, which isunderstood as being a refractive lens with diffractive structuresapplied thereto.

In the following, measures are described for distinguishing from oneanother the reflections produced by different surfaces on the lightsensor.

If the light paths of the measuring light that are associated with thedifferent image planes are separated from one another at least at onelocation of the measuring light beam path, it is possible to introduceinto those light paths filters which make the reflectionsdistinguishable. Such filters can be colour filters or polarisationfilters, for example. Instead of filters, it is also possible to useswitchable optical elements by means of which the light path can beinterrupted. In this manner it can be ensured that, at a given time,only the measuring light associated with a single image plane strikesthe optical system to be measured. That measuring light is then screenedoff by the switchable optical elements, and the measuring light requiredto measure the position of the next centre of curvature is allowed topass, and so on.

The reflections can also be distinguished if the images of an objectimaged by the imaging lens system and arranged in the object plane areoffset laterally on the light sensor. Such a lateral offset can beproduced, for example, by arranging the optical system so that it istilted by a tilt angle α relative to an optical axis of the imaging lenssystem. As a result, the centres of curvature are at different distancesfrom the optical axis of the imaging lens system. This has the resultthat the associated reflections, that is to say the images of an objectarranged in the object plane, are also at different distances from theoptical axis of the imaging lens system and as a result appear laterallyoffset on the light sensor.

If the imaging lens system additionally images the at least one objectplane into a third image plane which is different from the first and thesecond image plane, images of the object imaged by the imaging lenssystem can also be offset laterally relative to one another in twodirections on the light sensor.

With regard to the device, the object mentioned at the beginning isachieved by a device for measuring the positions of centres of curvatureof optical surfaces of a single- or multi-lens optical system, whichdevice comprises:

-   -   a) an imaging lens system which is configured to image at least        one, and preferably exactly one, object plane into a first image        plane and a second image plane which is different therefrom but        is situated in the same beam path;    -   b) a spatially resolving light sensor which is configured to        detect reflections of measuring light at optical surfaces of the        optical system;    -   c) an evaluation device which is configured to calculate the        actual position of a first and a second centre of curvature on        the basis of the reflections detected by the light sensor, after        the optical system has been so arranged that, taking into        consideration the refractive effect of any optical surface of        the optical system situated upstream in the beam path, a        supposed position of the first centre of curvature is situated        in the first image plane of the imaging lens system and a        supposed position of the second centre of curvature is situated        in the second image plane of the imaging lens system, and after        an object arranged in the object plane has been imaged        simultaneously or sequentially at the first and at the second        image plane by means of measuring light which strikes the        optical system from one side.

The evaluation device can be configured, when calculating the positionof a centre of curvature of an optical surface lying within the opticalsystem, to take into consideration mathematically the measured positionsof the centres of curvature of the optical surfaces lying between thatoptical surface and the imaging lens system.

The imaging lens system can be so designed that it does not compriseoptical elements which are movable in the axial direction.

The evaluation device can comprise a data storage means in which thereare stored data which relate to the allocation of positions of centresof curvature with locations on the light sensor. The reflections can bedetectable only in a single azimuthal angular position of the opticalsystem relative to the optical axis of the imaging system.

The imaging lens system can comprise two ancillary lens systems withdifferent focal lengths, the light paths of which are separated by firstbeam splitters arranged before the ancillary light systems in the lightpropagation direction and combined by beam combiners arranged after theancillary lens systems in the light propagation direction.

The imaging lens system can comprise at least one optical element whichhas different properties, in particular a different refractive power, inthe azimuthal direction.

Alternatively or in addition, the imaging lens system can comprise atleast one optical element which has different properties, in particulara different refractive power, in the radial direction. In addition, theimaging lens system can comprise a multi-focal diffractive lens or ahybrid lens. There comes into consideration in particular the use of animaging lens system which comprises an optical element with longitudinalchromatic aberration, whereby first and second measuring light thatdiffers in terms of wavelength is used for measuring the centres ofcurvature.

The images of an object imaged by the imaging lens system and arrangedin the object plane can be offset laterally on the light sensor. If theimaging lens system additionally images the at least one object planeinto a third image plane which is different from the first and thesecond image plane, the images of the object imaged by the imaging lenssystem can be offset laterally relative to one another in two directionson the light sensor.

The invention additionally provides a method for measuring the positionsof centres of curvature of optical surfaces of a plurality of single- ormulti-lens optical systems which are of substantially the sameconstruction, comprising the following steps:

-   -   a) imaging at least one object into a first and into a second        image plane;    -   b) so arranging a calibration test piece, which is of at least        substantially the same construction as the optical systems,        that, taking into consideration the refractive effect of any        optical surface of the optical system situated upstream in the        beam path, a supposed position of a first centre of curvature of        the calibration test piece is situated in the first image plane        and a supposed position of a second centre of curvature of the        calibration test piece is situated in the second image plane;    -   c) detecting the locations at which reflections of the measuring        light at optical surfaces of the calibration test piece strike        at least one spatially resolving light sensor;    -   d) so arranging one of the optical systems that, taking into        consideration the refractive effect of any optical surface of        the optical system situated upstream in the beam path, a        supposed position of a first centre of curvature of the one        optical system is situated in the first image plane of the        imaging lens system and a supposed position of a second centre        of curvature of the one optical system is situated in the second        image plane of the imaging lens system;    -   e) detecting the locations at which reflections of the measuring        light at the optical surfaces of the one optical system strike        the at least one spatially resolving light sensor, wherein no        further detection of locations at which reflections of the        measuring light at the optical surfaces of the one optical        system strike the at least one spatially resolving light sensor        is carried out in a different angular position of the one        optical system, and wherein no optical elements of at least one        imaging lens system which images the at least one object at the        image planes are moved axially;    -   f) determining the first and the second centre of curvature of        the one optical system on the basis of the locations detected in        step e) and taking into consideration the locations detected in        step c) for the calibration test piece;    -   g) repeating steps d) to f) for another of the optical systems.

This aspect of the invention is based on the finding that it is possibleto dispense with measuring the optical system in a plurality ofazimuthal angular positions, as is conventionally necessary, if, beforethe centres of curvature are measured, a calibration measurement iscarried out using a calibration test piece. The calibration test pieceis of at least substantially the same construction as the opticalsystems for which the positions of the centres of curvature are actuallyto be measured. “Substantially the same” is here understood as meaningthat the optical systems have the same optical design but can differslightly from one another as a result of material faults, alignmenttolerances or other manufacturing errors. This calibration measurementprovides an allocation of locations on the light sensor with actualpositions of centres of curvature.

As a result, the measuring operation as a whole can be carried outextremely quickly. The method can thereby also be used in connectionwith the alignment or quality testing of optical systems which areproduced in large numbers in an industrial process.

The plurality of image planes can, as described above, be provided by animaging lens system which images at least one, and preferably exactlyone, object plane into a first image plane and a second image planewhich is different therefrom but is situated in the same beam path.However, it is also possible to use measuring devices known in the priorart, in which the image planes are produced in beam paths that areseparate from one another.

One possibility for a calibration measurement consists in measuring thepositions of the centres of curvature of the calibration test piecebeforehand or subsequently by means of an external measuring device.These actual positions of the centres of curvature are then associatedwith locations at which reflections are detected on the at least onelight sensor.

Instead of using an external measuring device, measurement of thepositions of the centres of curvature can also be carried out in thesame measuring device as is later used for measuring the plurality ofoptical systems. To that end, it is merely necessary that the measuringdevice has a turntable. The calibration test piece can then be measuredin a plurality of azimuthal angular positions, as is known in the priorart. The locations at which reflections form on the at least one lightsensor then lie on a circular path whose mid-point coincides with theaxis of rotation of the turntable. The radius of the circle gives thedistance of the centre of curvature from the axis of rotation.

A further possibility for the calibration measurement consists inmeasuring, by means of an external measuring system, the locations atwhich images of an object imaged by an imaging lens system form in thefirst and in the second image plane. Imaging errors of the imaging lenssystem can thus be detected directly and can be taken into considerationmathematically when measuring the positions of the centres of curvature.

The various features of novelty which characterize the invention arepointed out with particularity in the claims annexed to and forming apart of the disclosure. For a better understanding of the invention, itsoperating advantages, specific objects attained by its use, referenceshould be had to the drawings and descriptive matter in which there areillustrated and described preferred embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWING

Further features and advantages of the invention will become apparentfrom the following description of embodiments with reference to thedrawings, in which:

FIG. 1 is a meridional section through a multi-lens optical system inwhich all the lenses are aligned perfectly with a reference axis;

FIG. 2 shows a single lens from the optical system shown in FIG. 1, butwhich is tilted relative to the reference axis;

FIG. 3 is a schematic representation of the centres of curvature of amulti-lens optical system;

FIG. 4 is a schematic representation as in FIG. 3, but wherein thecentres of curvature lie on a straight line different from the referenceaxis;

FIG. 5 is a meridional section through an autocollimator according tothe prior art in the measurement of a spherical lens aligned exactlywith the reference axis;

FIG. 6 shows the autocollimator of FIG. 5 but with a spherical lens thatis off-centre;

FIG. 7 is a meridional section through a measuring device according tothe invention according to a first embodiment, wherein an ancillary lenssystem has a plurality of beam splitters;

FIGS. 8a to 8c show the images of a crossed-slit diaphragm on a lightsensor of the measuring device shown in FIG. 7;

FIG. 9 is a meridional section through a measuring device according tothe invention according to a second embodiment, in which an ancillarylens system divides the measuring light aperture into a plurality ofazimuthal segments;

FIG. 10 is a top view of an arrangement of segment-like zoom lenses ofthe measuring device shown in FIG. 9;

FIG. 11 is a top view of an arrangement of three colour filters of themeasuring device shown in FIG. 9;

FIG. 12 shows images in different colours of a crossed-slit diaphragm onthe light sensor of the measuring device shown in FIG. 9;

FIG. 13 is a meridional section through a measuring device according tothe invention according to a third embodiment, in which an ancillarylens system divides the measuring light aperture into a plurality ofradial rings;

FIG. 14 is a top view of an arrangement of three zoom lenses ofdifferent diameters of the measuring device shown in FIG. 14;

FIG. 15 is a top view of an arrangement of three colour filters of themeasuring device shown in FIG. 13;

FIG. 16 is a meridional section through a measuring device according tothe invention according to a fourth embodiment, in which a diffractiveoptical element divides the measuring light aperture into different andoverlapping partial light paths in dependence on wavelength;

FIG. 17 is a meridional section through a modification of the fourthembodiment shown in FIG. 16, in which two different objects are imagedseparately, but in a common beam path, at the two image planes;

FIG. 18 is a flow diagram for explaining important steps of the methodaccording to the invention.

DETAILED DESCRIPTION OF THE INVENTION 1. Introduction

FIG. 1 shows, in a meridional section, an optical system, designated 10as a whole, which comprises seven lenses L1 to L7. The two lenses L3 andL4 are joined together without a gap and form a doublet used as anachromatic lens. The lenses L1 to L7 have a cylindrically ground lensedge 12, which in each case is housed in a lens mount (not shown).

In the ideal case, the lenses L1 to L7 are so aligned that their opticalaxes all lie on a common reference axis 14, which at the same time isthe axis of symmetry of the cylindrical lens edges. The reference axis14 is then generally referred to as the optical axis of the opticalsystem 10.

In real optical systems, however, deviations from such an idealalignment occur due to manufacturing and mounting tolerances. FIG. 2shows, for lens L5 by way of example, how a slight (but in FIG. 2exaggerated) tilting of the lens L5 in the lens mount affects thecentering. It is here assumed that the two lens surfaces S51 and S52 ofthe lens L5 are spherical and have centres of curvature which aredesignated K51 and K52 in FIG. 2. The centres of curvature K51 and K52define the optical axis of the lens L5, which optical axis is shown by abroken line 16 in FIG. 2. As a result of this definition, the opticalaxis 16 always runs perpendicular to the spherical optical surfaces S51,S52 of the lens L5.

In the case of aspherical lenses, the optical axis is defined by thecentres of curvature of the spherical portion of the aspherical lenssurfaces.

Tilting of the lens L5 can be caused, for example, by the lens L5 notbeing inserted correctly into its lens mount. A possible reason for thisis, for example, that the lens edge 12 was not ground in such a mannerthat its axis of symmetry is in line with the optical axis 16 of thelens L5.

In order to align the lens L5 correctly with the reference axis 14 ofthe optical system 10, the lens L5 would have to be tilted andoptionally additionally displaced perpendicularly to the reference axis14 so that the optical axis 16 is in line with the reference axis 14, ashas been assumed in FIG. 1.

In the case of a multi-lens optical system, as is shown in FIG. 1, theoptical axes of the individual lenses are generally distributed more orless unevenly relative to the reference axis 14, depending on thequality of the centering. This is shown by way of example in FIG. 3 foran optical system having four lenses with centres of curvature K11, K12,K21, K22, K31, K32 and K41, K42; the optical axes of the four lenses aredenoted 161, 162, 163, 164. In order to improve the centering of thelenses in such an optical system, several lenses must be tilted and/ordisplaced in translation in order that all the optical axes 161, 162,163, 164 are in line with the reference axis 14.

Sometimes, as is shown in FIG. 4, it can also happen that, although theoptical axes of the lenses are arranged (at least approximately) on acommon optical axis 16′, that axis is not in line with the referenceaxis 14. In such a case, it can be more convenient not to realign theindividual lenses but to fit the optical system as a whole into ahigher-level unit in such a manner that it is aligned in thehigher-level unit not with respect to its reference axis 14, which canbe defined, for example, by lens mounts or an objective housing, butwith respect to its optical axis 16′.

In order, where appropriate, to be able to realign individual lenses ofan optical system or the optical system as a whole, but also for routinequality control, a measuring device according to the invention is used,with which the positions of the centres of curvature of the opticalsurfaces can be measured with high accuracy. From the positions of thecentres of curvature, the locations of the optical axes of theindividual lenses and the deviation thereof from a reference axis 14 canbe determined. It is further possible to determine parameters derivedtherefrom, for example the radii of curvature of the optical surfaces.In the following section 2, the structure of a conventionalautocollimator will first be explained with reference to FIGS. 5 and 6,before a measuring device according to the invention and the measuringmethod which can be carried out therewith are discussed in section 3.

2. Structure of an Autocollimator

The autocollimator shown in a meridional section in FIG. 5 anddesignated 22 as a whole comprises a light source 38 which illuminates acrossed-slit diaphragm 40 arranged in an object plane 39 with measuringlight 41. The measuring light 41 leaving the crossed-slit diaphragm 40is directed via a beam splitter 42 to a collimator lens 44 and leavesthe collimator lens as a beam cluster. A zoom lens 46, which is movablealong an optical axis 34 of the autocollimator, focuses the collimatedmeasuring light 41 in a focal plane. Because a real image of thecrossed-slit diaphragm 40 forms there, that focal plane will be referredto in the following as the image plane 47.

On the rear side of the beam splitter 42 there is arranged an imagesensor 50, which is here understood as being a light-sensitive spatiallyresolving sensor. Suitable as the image sensor are, for example, CCD orCMOS sensors known per se.

The function of the autocollimator 22 will be explained in the followingwith reference to FIGS. 5 and 6. The measuring light 41 leaving theautocollimator 22 is here directed at a test piece, which for the sakeof simplicity is a sphere 52. If the mid-point 54 of the sphere 52, andthus the centre of curvature of its surface 56, lies exactly in theimage plane 47 of the autocollimator 22, the measuring light from theautocollimator 22 strikes the surface 56 of the sphere 52perpendicularly. Consequently, the measuring light 41 is reflected backon itself at the surface 56 of the sphere, passes through the zoom lens46, the collimator lens 44 and, for a large part, also through the beamsplitter 42 and produces an image of the crossed-slit diaphragm 40 onthe image sensor 50. If the mid-point 54 of the sphere 52 is situated onthe optical axis 34 of the autocollimator, the image of the crossed-slitdiaphragm 40 on the image sensor 50 is likewise centred on the opticalaxis 34.

FIG. 6 shows the beam path in the case where the sphere 52 has beendisplaced perpendicularly to the optical axis 34 of the autocollimator22. As a result of this displacement, the light beams no longer strikethe surface 56 of the sphere 52 perpendicularly and are therefore alsonot reflected back on themselves. The reflected measured light 41, shownby the broken line in FIG. 6, therefore produces on the image sensor 50an image 60 of the crossed-slit diaphragm 40 that is off-centre relativeto the optical axis 34.

Because the off-centre of the sphere 52 ultimately means that theportion of its surface 56 facing the autocollimator 22 is tilted, theautocollimator 22 ultimately measures the angle enclosed by the surface56 of the sphere 52 and the optical axis 34. The autocollimatortherefore constitutes an angle-measuring device in the broader sense.Accordingly, other contactless angle-measuring devices can also be usedinstead of the autocollimator 22 for the measuring device describedhereinbelow.

In the case of lenses with spherical surfaces, this measuring operationfunctions in the same manner, except that the measurement yields not theposition of the mid-point of a sphere, as in the case of a sphere, butthe position of the centre of curvature of the spherical surface inquestion. The centre of curvature of the spherical portion of asphericaloptical surfaces can also be measured in this manner.

3. Structure of a Measuring Device According to the Invention

In the following, the structure of a measuring device 60 according tothe invention will be explained with reference to FIG. 7. The measuringdevice 60 comprises a computing unit 63 and the autocollimator 22described hereinbefore with reference to FIGS. 5 and 6, in which themovable zoom lens 46 has, however, been replaced by a lens system 62.

The lens system 62 in this embodiment comprises a first beam splitter 66a, a second beam splitter 66 b and a first deflecting mirror 67. Thefirst beam splitter 66 a divides the light path into a first partiallight path 68 a and a further light path, which is divided by the secondbeam splitter 66 b into a second partial light path 68 b and a thirdpartial light path 68 c. The first deflecting mirror 67 deflects thethird partial light path 68 c in such a manner that a movement sectionis formed, in which the three partial light paths 68 a, 68 b and 68 cextend parallel to one another. In this movement section, a first, asecond and a third zoom lens 46 a, 46 b and 46 c are movably arranged inthe partial light paths 68 a, 68 b and 68 c, as is indicated by arrowsin FIG. 7. The zoom lenses 46 a, 46 b and 46 c each assume in thepartial light paths 68 a, 68 b and 68 c the function of the zoom lens 46of the autocollimator 22 shown in FIGS. 5 and 6. In addition, in theregion of the movement section, a first shutter 69 a, a second shutter69 b and a third shutter 69 c are arranged in the partial light paths 68a, 68 b and 68 c. The shutters 69 a, 69 b and 69 c can be in the formof, for example, slit diaphragms or LCD diaphragms and are to have theproperty of quickly being able to fully close or fully open the partiallight path 68 a, 68 b or 68 c in question.

The lens system 62 further comprises a second beam combiner 70 b whichcombines the second partial light path and the third partial light path68 c deflected by a further deflecting mirror 71 to form one light path,and a first beam combiner 70 a which combines that light path with thefirst partial light path 68 a and thereby superposes them to form acommon light path. By superposing the partial light paths 68 a, 68 b and68 c in that manner, the lens system 62 simultaneously produces a firstimage plane 47 a, which is produced by the measuring light 41 in thefirst partial light path 68 a, a second image plane 47 b, which isproduced by the measuring light 41 in the second partial light path 68b, and a third image plane 47 c, which is produced by the measuringlight 41 in the third partial light path 68 c. The three image planes 47a, 47 b, 47 c are arranged axially behind one another, so that threecorrespondingly axially staggered images of the crossed-slit diaphragm40 are obtained.

If all the zoom lenses 46 a, 46 b and 46 c are situated at the sameheight, the distance between the image planes 47 a and 47 b isapproximately equal to the axial distance between the first and secondbeam combiners 70 a and 70 b. Correspondingly, the distance between theimage planes 47 b and 47 c is approximately equal to the axial distancebetween the second beam combiner 70 b and the second deflecting mirror71. By moving the individual zoom lenses 46 a, 46 b and 46 c axially,the image planes 47 a, 47 b and 47 c within a region, which is definedby the length of the possible movement path of the zoom lenses 46 a, 46b and 46 c in movement section, can be displaced.

The measuring device according to the invention additionally includes atest piece holder 72, which is fastened to a holding ring 74. In theembodiment shown, the test piece P is a doublet having two lensescemented together. The test piece consequently has three opticalsurfaces S1, S2 and S3 with centres of curvature K1, K2 and K3.

4. Measuring Method

The measuring method according to the invention will be described ingreater detail in the following.

a) Calibration

Before the first measurement, the measuring device 60 should becalibrated, because only then can the highest measurement accuraciesgenerally be achieved.

In the calibration measurement, a calibration test piece whose centre ofcurvature is accurately known is inserted into the test piece holder 72.The calibration test piece can to that end have been measured by meansof an external measuring device, for example. The calibration test pieceis preferably an optical system of the same type as that which is laterto be measured in a larger number. The calibration test piece ismeasured in the measuring device 60 in the manner described hereinbelowunder b). The measured values so obtained are then correlated with theknown centres of curvature.

In this manner there are obtained calibration values with which latermeasured values on real test pieces can be corrected in order to be ableto take account of material faults or alignment errors of the opticalelements and of the test piece holder 56 of the measuring device 60.

In addition, it is possible to use for the calibration measurement acalibration test piece in which the positions of the centres ofcurvature of the optical surfaces are determined not highly accuratelyin an external measuring device but in the measuring device 60. To thatend, the calibration test piece with the unknown centre of curvature ismeasured by means of the measuring device 60 in a plurality of differentazimuthal angular positions. For this purpose, the measuring device 60must have, instead of the holding ring 74, a turntable which isrotatable about an axis of rotation which preferably coincidesapproximately with the optical axis 34 of the autocollimator 22. Theposition of the centre of curvature can then be derived from themid-point of the circular path on which the image of the crossed-slitdiaphragm 40 on the image sensor 50 moves during rotation of thecalibration test piece about the optical axis 34. When real test piecesare measured, measurement is carried out in only one angular position ofthe turntable in each case. The measuring results so obtained are thencorrected as described above using the calibration values.

b) Measuring the Positions of the Centres of Curvature

In order to measure the positions of the centres of curvature K1, K2 andK3 of the optical surfaces S1, S2, S3 in the case of the multi-lens testpiece P, a plurality of measuring operations must be carried out insuccession, starting, for example, with the optical surface that isclosest to the autocollimator 22. As can be seen in FIG. 7, that surfaceis the surface S1. The centre of curvature K1 of the surface S1 isfurthest away from the lens system 62. Therefore, there is used for thispartial measurement measuring light 41 which takes the first partiallight path 68 a, since the region having the longest focal lengths isassociated therewith. To that end, the first shutter 69 a is opened andthe other two shutters 69 b, 69 c are closed.

Before the calibration measurement, the first zoom lens 46 a of theancillary lens system 62 a has preferably already been moved so that thefirst image plane 47 a lies in the vicinity of the centre of curvatureK1 expected on the basis of the design data. The measuring light 41 fromthe first partial light path 68 a, indicated by continuous lines in FIG.7, then strikes the surface S1 perpendicularly and is reflected back onitself. The location of the image 40 a′ of the crossed-slit diaphragm 40on the light sensor 50 is detected, as is illustrated by FIG. 8a . Theposition of the centre of curvature K1 is determined from that location,taking into consideration the previously stored calibration values, andstored in a data storage means of the evaluation device 63.

In a second step, the position of the centre of curvature K2 of thesecond surface S2 is measured. The centre of curvature K2 of the surfaceS2 lies between the centres of curvature K1 and K3 of the surfaces S1and S3. Therefore, there is used for this measuring step measuring light41 that takes the second partial light path 68 b, since the region withthe medium focal lengths is associated therewith. To that end, thesecond shutter 69 b is opened and the other two shutters 69 a and 69 care closed. This measuring light is indicated in FIG. 7 by long-dashedlight beams.

Before the calibration measurement, the second zoom lens 46 b of theancillary lens system 62 has preferably already been moved so that thesecond image plane 47 b lies in the vicinity of the centre of curvatureK2 expected on the basis of the design data. The refractive effect ofthe first surface S1 of the test piece P has thereby already been takeninto consideration. If an image of the crossed-slit diaphragm 40 wereactually to form at the centre of curvature K2 of the surface S2, themeasuring light 41 would not strike the surface S2 perpendicularly as aresult of refraction at the first surface S1 situated upstream in thelight path. The refractive effect of the first surface S1 is thereforeto be taken into consideration mathematically, when determining theimage plane 47 b in which the crossed-slit diaphragm 40 is imaged inthis second measuring operation, so that the measuring light 41 strikesthe second surface S2 perpendicularly, as is shown in FIG. 7. In otherwords, the image plane 47 b is not arranged where the centre ofcurvature K2 of the second surface S2 is actually situated but where itappears as seen from the second surface S2, if the centre of curvatureK2 is considered through the optical surface S1. The location of theimage 40 b′ of the crossed-slit diaphragm 40 on the light sensor 50 isthen detected, as illustrated by FIG. 8b . The position of the centre ofcurvature K2 is determined from that location, taking into considerationthe previously stored calibration values, and stored in a data storagemeans of the evaluation device 63.

The position of the centre of curvature K3 of the third surface S3 ismeasured in the same manner. To that end, measuring light 41 that hasfollowed only the third partial light path 68 c is used. When adjustingthe third zoom lens 46 c, mathematical consideration was given to therefractive effect not only of the first surface S1 but also of thesecond surface S2, for which reason it is here too not the actual centreof curvature that lies in the image plane 47 c but only an apparentcentre of curvature K3′. The position of the centre of curvature K3 isdetermined from the location, shown in FIG. 8c , of the image 40 c′ ofthe crossed-slit diaphragm 40 on the light sensor 50, taking intoconsideration the previously stored calibration values, and stored in adata storage means of the evaluation device 63.

The sequence of the above-described steps can of course also be changedas desired, because the results of one measuring step are not requiredto carry out another measuring step. The effect of the optical surfacessituated upstream in the beam path can in each case also be taken intoconsideration mathematically at the end. Accordingly, the measuringdevice 60 ultimately measures for the optical surfaces situateddownstream not the real but only the apparent positions of the centresof curvature.

Because the shutters 69 a, 69 b and 69 c are switchable very quickly,the three measuring steps described above can be carried out in a veryshort time, for example in less than one second. The positions of thecentres of curvature K1, K2 and K3 can thus be measured very quickly,provided that the image planes 47 a, 47 b and 47 c have been brought tothe correct axial positions beforehand by means of the zoom lenses 46 a,46 b and 46 c. This quick measuring operation is advantageous inparticular when the next measuring task consists in measuring a testpiece P′ of the same type, which in principle has the same design data,such as refractive indices, dimensions and radii of curvature, but thecentres of curvature can lie at slightly different positions due tomanufacturing tolerances. The test piece P′ is then simply replaced bythe test piece P. The subsequent measuring operation can then be carriedout without any movements of zoom lenses or other components, apart fromthe operations of closing the shutters 69 a, 69 b, 69 c. If the testpieces are exchanged by means of a robot arm, the measuring timerequired for complete measurement of the positions of the centres ofcurvature can be within the order of magnitude of a few seconds.

5. Alternative Embodiments

a) Azimuthal Division of the Measuring Light Aperture

FIG. 9 shows another embodiment of a measuring device according to theinvention in a representation based on FIG. 7.

In this example, the entire aperture of the measuring light 41 isdivided into three segments each of 120°. Each of these segments definesa partial light path and contains an axially movable zoom lens 46 a, 46b and 46 c. FIG. 10 shows a top view of the three zoom lenses 46 a, 46 band 46 c. They are not rotationally symmetrical but each consist only ofa lens segment with an azimuth angle of 120°. If combined to form acomplete aperture of 360°, the zoom lenses 46 a, 46 b and 46 c would,however, be rotationally symmetrical.

The focal lengths of the zoom lenses 46 a, 46 b, 46 c are different. Inaddition, the zoom lenses 46 a, 46 b, 46 c can be moved independently ofone another along the optical axis 34, as is indicated in FIG. 9 bydouble-headed arrows. The second zoom lens 46 b is not visible in thisrepresentation because it is situated solely in the half of themeasuring device 60 shown in section that faces the observer.

By means of the three segment-like zoom lenses 46 a, 46 b, 46 c, threedifferent image planes 47 a, 47 b and 47 c can be producedsimultaneously as in the embodiment described above, which image planesare situated in the vicinity of the actual positions of the centres ofcurvature or of the apparent positions of the centres of curvature,taking into consideration the refraction of surfaces situated upstream.

There are no shutters 69 a, 69 b, 69 c in this embodiment. The images ofthe crossed-slit diaphragm 40, which form on the light sensor 50 by thereflections at the optical surfaces S1, S2 and S3 of the test piece P,therefore always appear simultaneously. In order to be able todistinguish the images from one another and associate them with thecentres of curvature K1, K2 and K3 of the test piece P, three colourfilters 75 a, 75 b and 75 c are arranged in the collimated beam path ofthe ancillary lens systems 62 a, 62 b, 62 c, which colour filters eachhave the shape of a segment, as illustrated in FIG. 11 in a top view.The colour filters 75 a, 75 b, 75 c are so oriented that only light of aspecific colour (that is to say of a specific wavelength range) everstrikes the zoom lenses 46 a, 46 b and 46 c. The images 40 a′, 40 b′ and40 c′ of the crossed-slit diaphragm 40 produced on the light sensor 50accordingly also differ in colour and can thus easily be distinguishedfrom one another, as is illustrated by FIG. 12.

b) Radial Division of the Measuring Light Aperture

FIG. 13 shows a representation, based on FIGS. 7 and 9, of a measuringdevice according to a further embodiment of the invention.

Here too, different partial light paths 68 a, 68 b and 68 c areproduced, with which different image planes 47 a, 47 b are associated;in FIG. 13, the partial light path 68 c and the image plane 47 cassociated therewith are not shown for the purpose of clarity. Unlike inthe embodiment shown in FIG. 9, however, the partial light paths 68 a,68 b and 68 c are produced not by an azimuthal division of the measuringlight aperture but by a radial division.

To that end, three lenses are arranged one behind the other in theancillary lens system 62, the diameters of which lenses differconsiderably. The diameters are such that a portion of the measuringlight 41 passes through only the first zoom lens 46 a, a second portionof the measuring light 41 passes only through the first zoom lens 46 aand the second zoom lens 46 b, and a third portion of the measuringlight 41 passes through all three zoom lenses 46 a, 46 b and 46 c. Thethree zoom lenses 46 a, 46 b and 46 c can be moved individually, as isindicated in FIG. 13 by double-headed arrows. In a housing 78 of theancillary lens system 62, the two smaller zoom lenses 46 b and 46 c areheld by thin rods 80 b and 80 c, as is shown in FIG. 14 in a top view.The rods 80 b, 80 c are so thin that they obstruct only a negligibleportion of the measuring light 41 as it passes through the ancillarylens system 62.

In this embodiment, therefore, the image planes 47 a, 47 b and the imageplane 47 c that is not shown are produced by radial segments of theaperture of the measuring light 41 which are different and do notoverlap in the region of the image planes.

Correspondingly, the colour filters 75 a, 75 b and 75 c in thisembodiment are also not divided into segments but have the form ofconcentric rings or—in the case of the third colour filter 75 c—of acircular disc. This arrangement of the colour filters 75 a, 75 b and 75c in the collimated beam path of the measuring light 41 ensures that themeasuring light 41 focused in the three image planes 47 a, 47 b and 47 chas different colours, so that here too the images of the crossed-slitdiaphragm 40 on the light sensor 50 can be distinguished from oneanother on the basis of colour.

c) Diffractive Optical Element

FIG. 16 shows, in a representation based on FIGS. 7, 9 and 13, ameasuring device according to the invention according to a differentembodiment, in which the ancillary lens system 62 has a diffractiveoptical element 46′. In addition, in the beam path of the measuringlight 41, for example between the light source 38 and the crossed-slitdiaphragm 40, there is a colour filter 82 which is permeable to light ofonly three narrow wavelength ranges, which preferably do not overlap. Inthe following, it is assumed that those wavelength ranges are located inthe visible spectrum, for which reason they are referred to in thefollowing as colours.

The diffractive optical element 46′ is so designed that it focuses theincident collimated light in different focal planes in dependence on thecolour, of which the focal planes 47 a and 47 b are shown in FIG. 16. Asin the case of a refractive lens with longitudinal chromatic aberration,different focal planes for different colours thus form simultaneously.Here too, the images of the crossed-slit diaphragm 40 on the imagesensor 50 can easily be distinguished from one another on the basis ofthe different colours.

By moving the diffractive optical element 46′ along the optical axis 34,the image planes 47 a, 47 b and 47 c can together be moved in the axialdirection. In this embodiment, the image planes 47 a, 47 b, 47 c can beadjusted individually and independently of one another only by replacingthe colour filter with a colour filter that is permeable to differentwavelength ranges. Unlike the other embodiments, however, differentnumbers of image planes can be produced by means of the diffractiveoptical element 46′ with very little outlay and without light losses,because the colour filter 82 and/or the diffractive optical element 46′simply have to be replaced. The measuring device 60 can thus readily bechanged from an operating mode in which only the positions of, forexample, two specific centres of curvature are to be measured, to anoperating mode in which, for example, ten centres of curvature are to bemeasured simultaneously.

FIG. 17 shows a modified embodiment in which the light path is dividedupstream of the beam splitter 42 into two partial light paths by meansof a second beam splitter 84. In a first partial light path, a firstlight source 38 a illuminates a first crossed-slit diaphragm 40 a via afirst wavelength filter 82 a which is permeable only to light of onecolour. In a second partial light path, a second light source 38 billuminates a second crossed-slit diaphragm 40 b via a second wavelengthfilter 82 b which is permeable only to light of a different colour.Exactly one wavelength filter 82 a or 82 b is thus associated with eachfocal plane 47 a, 47 b. As a result, the focal planes can be displacedeven more easily by replacing single wavelength filters individually.

Because in this embodiment the two diaphragms 40 a, 40 b are arranged indifferent object planes 39 a and 39 b, diaphragms with differentlyshaped diaphragm openings can be used. The images of the diaphragms onthe light sensor 50 can then easily be distinguished from one anothernot only by their colours but also by their shape. Consequently, acolour-insensitive light sensor 50 can also be used in this embodiment.

In the embodiment shown, the test piece P has only two optical surfacesS1 and S2. If test pieces with more than two optical surfaces are to bemeasured, it is possible, as in the embodiment shown in FIG. 16, to usecolour filters which are permeable to a plurality of wavelength rangeswhich do not overlap.

5. Important Method Steps

Important steps of the method according to the invention will bedescribed in the following with reference to the flow diagram shown inFIG. 18.

In a first step S1, an imaging lens system is provided which images atleast one object plane into a first object plane and a second objectplane different therefrom.

In a second step S2, the optical system is so arranged that, taking intoconsideration the refractive effect of any optical surface of theoptical system situated upstream in the beam path, a supposed positionof a first centre of curvature is situated in the first image plane ofthe imaging lens system and a supposed position of a second centre ofcurvature is situated in a second image plane of the imaging lenssystem.

In a third step S3, an object arranged in the object plane is imaged atthe first and at the second image plane by means of measuring light.

In a fourth step S4, reflections of the measuring light at opticalsurfaces of the optical system are detected by means of a spatiallyresolving light sensor.

In a fifth step S5, the actual positions of the first and of the secondcentre of curvature are calculated on the basis of the reflectionsdetected in the fourth step S4.

While specific embodiments of the invention have been shown anddescribed in detail to illustrate the inventive principles, it will beunderstood that the invention may be embodied otherwise withoutdeparting from such principles.

We claim:
 1. A method for measuring the positions of centres ofcurvature of optical surfaces of a single- or multi-lens optical system,comprising the following steps: a) providing an imaging lens systemwhich images at least one object plane into a first image plane and asecond image plane which is different from the first image plane,wherein the first image plane is produced by a first ancillary lenssystem having a first focal length and defining a first beam path, thesecond image plane is produced by a second ancillary lens system havinga second focal length that is different from the first focal length anddefining a second beam path that is different from the first beam path,b) simultaneously or sequentially imaging an object arranged in theobject plane at the first image plane and at the second image plane bymeans of measuring light which strikes the optical system from one side;c) detecting reflections of the measuring light at optical surfaces ofthe optical system by means of a spatially resolving light sensor; d)calculating the actual positions of the first centre of curvature and ofthe second centre of curvature on the basis of the reflections detectedin step c).
 2. The method of claim 1, comprising the step of arrangingthe optical system in such a manner that, taking into consideration arefractive effect of any optical surface of the optical system situatedupstream in the beam path, a supposed position of a first centre ofcurvature is situated in the first image plane of the imaging lenssystem and a supposed position of a second centre of curvature issituated in the second image plane of the imaging lens system.
 3. Themethod of claim 1, wherein a beam splitter, which is arranged, in alight propagation direction, in front of the first ancillary lens systemand of the second ancillary lens system, splits a beam path of incidentmeasuring light into the first beam path and the second beam path. 4.The method of claim 1, wherein a light combiner, which is arranged, in alight propagation direction, behind the first ancillary lens system andthe second ancillary lens system, combines the first beam path and thesecond beam path to form a common beam path in which the optical systemis arranged.
 5. The method of claim 1, wherein the first beam path andthe second beam path are parallel to each other.
 6. The method of claim1, wherein each of the first ancillary lens system and the secondancillary lens system comprises a zoom lens that is movably arranged inthe first beam path and the second beam path, respectively.
 7. Themethod of claim 1, wherein a first shutter is arranged in the first beampath, and a second shutter is arranged in the second beam path.
 8. Themethod of claim 7, wherein each of the first shutter and the secondshutter comprises a slit diaphragm or an LCD diaphragm.
 9. The method ofclaim 1, wherein, before the centres of curvature are measured, acalibration measurement is carried out, from which an allocation oflocations on the light sensor with centres of curvature is derived. 10.A device for measuring the positions of centres of curvature of opticalsurfaces of a single- or multi-lens optical system, comprising: a) animaging lens system which is configured to image at least one objectplane into a first image plane and simultaneously into a second imageplane which is different from the first plane, wherein the imaging lenssystem comprises a first ancillary lens system that has a first focallength, produces the first image plane and defines a first beam path, asecond ancillary lens system that has a second focal length that isdifferent from the first focal length, produces the second image planeand defines a second beam path that is different from the first beampath, b) a spatially resolving light sensor which is configured todetect reflections of measuring light at optical surfaces of the opticalsystem; c) an evaluation device which is configured to calculate theactual position of a first centre of curvature and of a second centre ofcurvature on the basis of the reflections detected by the light sensor,after an object arranged in the object plane has simultaneously orsequentially been imaged at the first image plane and at the secondimage plane by means of measuring light which strikes the optical systemfrom one side.
 11. The device of claim 10, comprising a beam splitter,which is arranged, in a light propagation direction, in front of thefirst ancillary lens system and of the second ancillary lens system,wherein the beam splitter splits a beam path of incident measuring lightinto the first beam path and the second beam path.
 12. The device ofclaim 10, comprising a light combiner, which is arranged, in a lightpropagation direction, behind the first ancillary lens system and thesecond ancillary lens system, wherein the light combiner combines thefirst beam path and the second beam path to form a common beam path inwhich the optical system is arranged.
 13. The device of claim 10,wherein the first beam path and the second beam path are parallel toeach other.
 14. The device of claim 1, wherein each of the firstancillary lens system and the second ancillary lens system comprises azoom lens that is movably arranged in the first beam path and the secondbeam path, respectively.
 15. The device of claim 10, wherein a firstshutter is arranged in the first beam path, and a second shutter isarranged in the second beam path.
 16. The device of claim 15, whereineach of the first shutter and the second shutter comprises a slitdiaphragm or an LCD diaphragm.
 17. The device of claim 10, wherein theevaluation device comprises a data storage means in which there arestored data relating to an allocation of positions of centres ofcurvature with locations on the light sensor.
 18. A device for measuringthe positions of centres of curvature of optical surfaces of a single-or multi-lens optical system, comprising: a) an imaging lens systemwhich is configured to image, with the help of measuring light, at leastone object into a first image plane and into a second image plane whichis different from the first image plane, wherein the imaging lens systemcomprises a first lens and a second lens, wherein measuring light thatis focused in the first image plane passes only through the first lens,but not through the second lens, and wherein measuring light that isfocused in the second image plane passes only through the second lens,but not through the first lens; b) a light sensor which is configured todetect reflections of measuring light at optical surfaces of the opticalsystem; c) an evaluation device which is configured to calculate aposition of a first centre of curvature and of a second centre ofcurvature on the basis of the reflections detected by the light sensor.19. The device of claim 18, wherein the imaging lens system isconfigured to direct a first portion of the measuring light towards thefirst lens and simultaneously a second portion of the measuring lighttowards the second lens so that the first portion of the measuring lightis focused in the first image plane while the second portion of themeasuring light is focused in the second image plane.
 20. The device ofclaim 18, wherein the device is controlled such that the measuring lightis focused at a first time in the first image plane, but not in thesecond image plane, and at a later second time not in the first imageplane, but in the second image plane.